Water and Construction - Hydrogeology: Objectives, Methods, Applications - page 237

a number of buildings, and led to the fi ssuring and collapse of various
buildings and construction sites (Caudron, 2002).
The opposite effect, corresponding to abnormal drops in piezometric
levels, can also lead to the disorganization of certain buildings, due to
modifi cations in the characteristics of the soil supporting them. This was
the case, in particular, in several regions of France during the droughts
of 1989 to 1992, where numerous structures, built on clayey terrain, were
affected by multiple fi ssures, due to shrinkage linked to the drying of the
underlying soil.
2 INFLUENCE OF CONSTRUCTION IN WATER-BEARING
TERRAIN
Infrastructures implanted in aquifer formations perturb, in more or less
permanent ways, the state and order of fl ow in the aquifer, by creating
blockages or reducing the cross-sectional area of fl ow, or, inversely, by
accentuating the drainage.
These situations will have repercussions on the work being done, and
require detailed studies in order to resolve problems with foundations
and stability. They can also have repercussions on the environment in the
construction site and require an examination of foreseeable impacts and
protection measures to be taken.
2.1 Role of hydraulic barrier
The simplest situation is that of a retaining wall built at the front of a
temporarily water-bearing terrain. This is a frequent case on clayey, marly
slopes thickened by a weathering mantle or by a scree cover of variable
thickness. It is common, especially when construction occurs during the dry
season, for the building to be under-dimensioned and often even completely
devoid of drainage. The rainy season and the sustained saturation of the soil
will often precipitate failure, either as a direct effect of hydraulic pressure, or
as an effect of the decrease in the angle of repose and the increased pressure
on the construction in the case of consolidated terrain.
The role of the hydraulic barrier is fully exercised when a building is set
well into a permanent aquifer over a representative length, which is often
the case in urban areas, where the use of the space below ground tends to
be intensifi ed in order to create basement levels (underground parking
lots) and subterranean passageways (subways). In certain sectors, the